1. Field of the Invention
The invention relates to a method for the recognition of natural skin during contact-free biometric identification of a person, as well as to a device for carrying out the method.
2. Description of Related Art
In the checking of authorization with regard to access to closed systems, which can be represented by room complexes or data networks, for example, biometric checks are being performed, to an increasing degree, for identification of the person authorized for access, since there is no risk that the individual biometric characteristics of an individual can be lost or passed on, as is the case with passwords or keys. In practice, the use of the papillary line patterns of the palms or the fingertips, as a biometric characteristic that is different for every individual and does not change, has proven itself, whereby methods are known with which these papillary line patterns can be optically detected in contact-free manner. In the case of these measurements, the papillary line pattern is evaluated as such, in other words the topology of the skin surface or, to state it differently, the pattern of the relief formed by the papillary ridges, is evaluated. In this connection, there is the problem that when the papillary line pattern is known, the measurement apparatus for detecting the biometric data can, in principle, be deceived by means of false copies that contain a reproduction of the papillary line pattern in accordance with the three-dimensional original, and which are possible, for example, in the form of two-dimensional reproductions, three-dimensional reproductions, or coverings on natural fingers.
WO 01/34 027 A2 discloses a method that serves not for biometric identification, but rather for the diagnosis of skin diseases, with a related device, wherein the skin is illuminated by means of an illumination ring during the examination of skin lesions, in order to take pictures of the skin lesion, to digitalize them and evaluate them, which images are generated by means of scattered light.
EP 0 359 554 A2 describes a method for the identification of persons, wherein optical fingerprints are determined, which are brought into contact with a glass plate, in other words the method of working is not contact-free, and the glass plate is exposed to manipulation attempts and attempts to damage it, because of the accessibility that is absolutely required. In addition to the fingerprints, in order to prevent forgeries, an evaluation takes place, at the same time, as to whether there is an offset between the irradiation point and the point at which the light enters into the measurement apparatus.
U.S. Pat. No. 5,598,843 describes a device with which light is radiated in by direct contact with the skin, by means of a first emitter, which light is detected by a second emitter, which is separated from the first emitter by means of a non-transparent wall.
U.S. Pat. No. 5,419,321 also shows a non-invasive but contact-requiring sensor for optical, quantitative determination of a substance in living tissue.